fork download 
  1. (defun reverse-integer (integer &key (radix 10))
  2.   (let ((sign (if (minusp integer) #'- #'+))
  3.         (i (abs integer)))
  4.     (loop for (q r) = (multiple-value-list (floor i radix))
  5.             then (multiple-value-list (floor q radix))
  6.           collect r into digits
  7.           until (zerop q)
  8.           finally (return (funcall sign
  9.                                    (reduce (lambda (a v) (+ (* a radix) v))
  10.                                            digits
  11.                                            :initial-value 0))))))
  12.  
  13. (defun palindromic-number-p (x &key (radix 10) include-negative-numbers)
  14.   (and (integerp x)
  15.        (or include-negative-numbers
  16.            (<= 0 x))
  17.        (or (<= 0 (abs x) 9)
  18.            (= x (reverse-integer x :radix radix)))))
  19.  
  20. (defun find-closest-palindromic-numbers (n &key (radix 10)
  21.                                                 include-negative-numbers)
  22.   (loop for u upfrom n
  23.         for d downfrom n
  24.         for r = (remove nil
  25.                         (list (if (palindromic-number-p u
  26.                                                         :radix radix
  27.                                                         :include-negative-numbers
  28.                                                         include-negative-numbers)
  29.                                   u)
  30.                               (if (palindromic-number-p d
  31.                                                         :radix radix
  32.                                                         :include-negative-numbers
  33.                                                         include-negative-numbers)
  34.                                   d)))
  35.         when (car r)
  36.           do (return (delete-duplicates (sort r #'<)))))
  37.  
  38.  
  39. (loop for s = (read-line nil nil)
  40.       for n = (and s (parse-integer s))
  41.       while s
  42.       do (format t "~{~D~^, ~}~%"
  43.                  (find-closest-palindromic-numbers n)))
  44.  
Success #stdin #stdout 0.01s 29268KB
comments (?)
stdin 
0
17
100
stdout 
0
22
99, 101
https://ideone.com/MvDoGf
language:
Common Lisp (sbcl 1.4.16)
created:
96 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!